First communication apparatus, second communication apparatus, method, program, recording medium, and system

ABSTRACT

In order to enable both a circuit scale of an apparatus that receives signals via antennas and a band of an interface between apparatuses to be small, a first communication apparatus according to the present invention includes: a reception processing unit configured to receive, from a second communication apparatus which receives signals via a plurality of antennas, channel related information related to a channel of signals received via the plurality of antennas; and a transmission processing unit configured to transmit, to the second communication apparatus, weight information related to receiving antenna weights by which the second communication apparatus multiplies signals received via the plurality of antennas, the weight information being generated based on the channel related information.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/494,618, filed on Sep. 16, 2019, which is a National Stage ofInternational Application No. PCT/JP2018/010027, filed on Mar. 14, 2018,which claims priority from Japanese Patent Application No. 2017-055726,filed on Mar. 22, 2017, the contents of all of which are incorporatedherein by reference in their entirety.

BACKGROUND Technical Field

The present invention relates to a first communication apparatus, asecond communication apparatus, a method, a program, a recording medium,and a system.

Background Art

As mobile communication is further advanced, a data transmission rate isimproved at a higher rate than available frequency bands are extended.Therefore, beamforming using a multi-element antenna, which allowsimprovement in a data transmission rate per frequency, has beenconsidered as an effective technique. In the beamforming, beams forreception (and transmission) are formed, based on channel estimates thatcan be acquired from received signals of respective antenna elementsincluded in a multi-element antenna.

For example, Patent Literature 1 discloses that a base stationdetermines transmit beamforming weights and performs transmitbeamforming, and a terminal apparatus determines receive beamformingweights and performs receive beamforming. For example, Patent Literature2 discloses that a terminal apparatus determines transmitting antennaweights and receiving antenna weights, based on reference signals from abase station, and reports information related to these weights to thebase station. Patent Literature 3 discloses an example of a structure ofa base station that is separated into a remote radio unit (RRU) and abase band unit (BBU).

CITATION LIST Patent Literature

[PTL 1] WO 2016/152916

[PTL 2] WO 2016/207929

[PTL 3] US 2014/0226736 A1

SUMMARY Technical Problem

For example, as described in Patent Literature 3, a base station may beseparated into an apparatus (e.g., an RRU) that receives signals viaantennas and another apparatus (e.g., a BBU), or the like. In such acase, for example, which apparatus performs processing such as channelestimation, generation of antenna weights, and multiplication of antennaweights, may affect a circuit scale of the apparatus (e.g., an RRU) anda band of an interface between the apparatuses. However, in PatentLiterature 3, which apparatus performs these processing is notdiscussed. Therefore, the technique described in Patent Literature 3cannot enable both a circuit scale of the apparatus and a band of aninterface between the apparatuses to be small.

An example object of the present invention is to provide a firstcommunication apparatus and a second communication apparatus that enableboth a circuit scale of an apparatus that receives signals via antennasand a band of an interface between apparatuses to be small.

Solution to Problem

A first communication apparatus according to an example aspect of thepresent invention includes a reception processing unit configured toreceive, from a second communication apparatus which receives signalsvia a plurality of antennas, channel related information related to achannel of signals received via the plurality of antennas, and atransmission processing unit configured to transmit, to the secondcommunication apparatus, weight information related to receiving antennaweights by which the second communication apparatus multiplies signalsreceived via the plurality of antennas, the weight information beinggenerated based on the channel related information.

A second communication apparatus according to an example aspect of thepresent invention includes a radio communication processing unitconfigured to receive signals via a plurality of antennas, atransmission processing unit configured to transmit, to a firstcommunication apparatus, channel related information related to achannel of signals received via the plurality of antennas, and receptionprocessing unit configured to receive, from the first communicationapparatus, weight information related to reception antenna weights, theweight information being generated based on the channel relatedinformation, wherein the radio communication processing unit isconfigured to multiply signals received via the plurality of antennas bythe receiving antenna weights.

A first method according to an example aspect of the present inventionincludes receiving, from a communication apparatus which receivessignals via a plurality of antennas, channel related information relatedto a channel of signals received via the plurality of antennas, andtransmitting, to the communication apparatus, weight information relatedto receiving antenna weights by which the communication apparatusmultiplies signals received via the plurality of antennas, the weightinformation being generated based on the channel related information.

A second method according to an example aspect of the present inventionincludes receiving signals via a plurality of antennas, transmitting, toa communication apparatus, channel related information related to achannel of signals received via the plurality of antennas, receiving,from the communication apparatus, weight information related toreception antenna weights, the weight information being generated basedon the channel related information, and multiplying signals received viathe plurality of antennas by the receiving antenna weights.

A first program according to an example aspect of the present inventionis a program that causes a processor to execute receiving, from acommunication apparatus which receives signals via a plurality ofantennas, channel related information related to a channel of signalsreceived via the plurality of antennas, and transmitting, to thecommunication apparatus, weight information related to receiving antennaweights by which the communication apparatus multiplies signals receivedvia the plurality of antennas, the weight information being generatedbased on the channel related information.

A second program according to an example aspect of the present inventionis a program that causes a processor to execute receiving signals via aplurality of antennas, transmitting, to a communication apparatus,channel related information related to a channel of signals received viathe plurality of antennas, receiving, from the communication apparatus,weight information related to reception antenna weights, the weightinformation being generated based on the channel related information,and multiplying signals received via the plurality of antennas by thereceiving antenna weights.

A first recording medium according to an example aspect of the presentinvention is a non-transitory computer readable recording medium havingrecorded thereon a program that causes a processor to execute receiving,from a communication apparatus which receives signals via a plurality ofantennas, channel related information related to a channel of signalsreceived via the plurality of antennas, and transmitting, to thecommunication apparatus, weight information related to receiving antennaweights by which the communication apparatus multiplies signals receivedvia the plurality of antennas, the weight information being generatedbased on the channel related information.

A second recording medium according to an example aspect of the presentinvention is a non-transitory computer readable recording medium havingrecorded thereon a program that causes a processor to execute receivingsignals via a plurality of antennas, transmitting, to a communicationapparatus, channel related information related to a channel of signalsreceived via the plurality of antennas, receiving, from thecommunication apparatus, weight information related to reception antennaweights, the weight information being generated based on the channelrelated information, and multiplying signals received via the pluralityof antennas by the receiving antenna weights.

A system according to an example aspect of the present inventionincludes a first communication apparatus and a second communicationapparatus, wherein the second communication apparatus is configured toreceive signals via a plurality of antennas, and transmit, to the firstcommunication apparatus, channel related information related to achannel of signals received via the plurality of antennas, wherein thefirst communication apparatus is configured to receive the channelrelated information from the second communication apparatus, andtransmit, to the second communication apparatus, weight informationrelated to receiving antenna weights, the weight information beinggenerated based on the channel related information, and wherein thesecond communication apparatus is configured to receive the weightinformation from the first communication apparatus, and multiply signalsreceived via the plurality of antennas by the receiving antenna weights.

A third method includes, in a second communication apparatus, receivingsignals via a plurality of antennas, and transmitting, to a firstcommunication apparatus, channel related information related to achannel of signals received via the plurality of antennas, in the firstcommunication apparatus, receiving the channel related information fromthe second communication apparatus, and transmitting, to the secondcommunication apparatus, weight information related to receiving antennaweights, the weight information being generated based on the channelrelated information, and, in the second communication apparatus,receiving the weight information from the first communication apparatus,and multiplying signals received via the plurality of antennas by thereceiving antenna weights.

Advantageous Effects of Invention

According to an example aspect of the present invention, both a circuitscale of an apparatus that receives signals via antennas and a band ofan interface between apparatuses can be small. Note that, according toan example aspect of the present invention, instead of or together withthe above effect, other effects may be exerted.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory diagram for describing an example of aconfiguration of a base station using a multi-element antenna;

FIG. 2 is an explanatory diagram for describing a first processingarrangement case of the base station;

FIG. 3 is an explanatory diagram for describing a second processingarrangement case of the base station;

FIG. 4 is an explanatory diagram illustrating an example of a schematicconfiguration of a system according to a first example embodiment;

FIG. 5 is an explanatory diagram illustrating an example of a schematicconfiguration of the base station according to the first exampleembodiment;

FIG. 6 is a block diagram illustrating an example of a schematicconfiguration of a digital apparatus according to the first exampleembodiment;

FIG. 7 is a block diagram illustrating an example of a schematicconfiguration of a radio apparatus according to the first exampleembodiment;

FIG. 8 is an explanatory diagram for describing a schematic example ofradio communication processing of the first example embodiment;

FIG. 9 is an explanatory diagram for describing a first example ofchannel estimation and weight information generation of the firstexample embodiment;

FIG. 10 is an explanatory diagram for describing an example of referencesignals of the first example embodiment;

FIG. 11 is an explanatory diagram for describing an example oftransmission of reference signals of the first example embodiment;

FIG. 12 is an explanatory diagram for describing a second example ofchannel estimation and weight information generation of the firstexample embodiment;

FIG. 13 is a sequence diagram for describing an example of a schematicflow of radio communication processing of the first example embodiment;

FIG. 14 is a sequence diagram for describing an example of a schematicflow of processing of transmission and/or reception of channel relatedinformation and weight information according to the first exampleembodiment;

FIG. 15 is an explanatory diagram illustrating an example of a schematicconfiguration of a system according to a second example embodiment;

FIG. 16 is a block diagram illustrating an example of a schematicconfiguration of a first communication apparatus according to the secondexample embodiment; and

FIG. 17 is a block diagram illustrating an example of a schematicconfiguration of a second communication apparatus according to thesecond example embodiment.

DESCRIPTION OF THE EXAMPLE EMBODIMENTS

Hereinafter, example embodiments of the present invention will bedescribed in detail with reference to the accompanying drawings. Notethat, in the Specification and drawings, elements to which the similardescriptions are applicable are denoted by the same reference signs, andoverlapping descriptions may hence be omitted.

Descriptions will be given in the following order.

1. Related Art

2. Overview of Example Embodiments

3. First Example Embodiment

-   -   3.1. Configuration of System    -   3.2. Configuration of Digital Apparatus    -   3.3. Configuration of Radio Apparatus    -   3.4. Technical Features    -   3.5. Example Alteration

4. Second Example Embodiment

-   -   4.1. Configuration of System    -   4.2. Configuration of First Radio Apparatus    -   4.3. Configuration of Second Radio Apparatus    -   4.4. Technical Features

1. Related Art

First, with reference to FIG. 1 to FIG. 3 , related art will bedescribed. Note that, of course, the related art described herein mayalso be included in example embodiments of the present invention.

Example of Configuration of Base Station Using Multi-Element Antenna

FIG. 1 is an explanatory diagram for describing an example of aconfiguration of a base station 50 using a multi-element antenna.

Reception Processing

Radio received signals (N series of radio received signals) of N antennaelements 51 included in a multi-element antenna are converted into Nseries of reception baseband signals on a time axis by a transmissionand/or reception unit 53, and are further converted into N series ofreceived signals on a frequency axis by a fast Fourier transform (FFT)unit 55. Further, the N series of received signals are multiplied by areceiving antenna weight matrix having M rows and N columns by anantenna weight multiplication unit 57. As a result, M series of receivedsignals (i.e., received signals of M layers) are output. The M series ofreceived signals are demodulated by a demodulation unit 59, and arefurther decoded by a decoding unit 61.

A channel estimation unit 63 performs channel estimation, based onreference signals included in the N series of received signals, whichare an output of the FFT unit 55. In this manner, N series of channelestimates are generated, and are then output. Further, the antennaweight generating unit 65 generates the receiving antenna weight matrixhaving M rows and N columns, based on the N series of channel estimates.Then, the receiving antenna weight matrix is used by the antenna weightmultiplication unit 57 as described above. Note that the antenna weightgenerating unit 65 may also generate a transmitting antenna weightmatrix having N rows and L columns, based on the N series of channelestimates.

Transmission Processing

Transmission signals are first coded by a coding unit 71, and are thenmodulated by a modulation unit 73. As a result, the transmission signalsare turned into L series of transmission signals (transmission signalsof L layers). The L series of transmission signals are multiplied by thetransmitting antenna weight matrix having N rows and L columns by anantenna weight multiplication unit 75, so as to be turned into N seriesof transmission signals on a frequency axis. The N series oftransmission signals on a frequency axis are converted into N series ofbaseband signals on a time axis by an inverse fast Fourier transform(IFFT) unit 77, and are further converted into N series of radiotransmission signals by the transmission and/or reception unit 53. Then,the N series of radio transmission signals are transmitted from the Nantenna elements included in the multi-element antenna.

Processing Arrangement in Base Station

In actual implementation, for example, the base station 50 in theexample of FIG. 1 is divided into a radio apparatus including thetransmission and/or reception unit 53, and a digital apparatus includingthe demodulation unit 59, the decoding unit 61, the coding unit 71, andthe modulation unit 73. For example, the radio apparatus is arrangedimmediately close to the multi-element antenna, the digital apparatus isarranged indoors inside a station, and the radio apparatus and thedigital apparatus are connected to each other with an optical fibercable.

Here, a case (first processing arrangement case) where the antennaweight multiplication units 57 and 75 and the antenna weight generatingunit 65 are arranged in a digital apparatus, and a case (secondprocessing arrangement case) where the antenna weight multiplicationunits 57 and 75 and the antenna weight generating unit 65 are arrangedin a radio apparatus are considered.

First Processing Arrangement Case

FIG. 2 is an explanatory diagram for describing the first processingarrangement case of the base station 50. In this example, the antennaweight multiplication units 57 and 75, the channel estimation unit 63,and the antenna weight generating unit 65 are arranged in a digitalapparatus 90, not in a radio apparatus 80.

In the first processing arrangement case, a circuit scale of the radioapparatus 80 is small, and thus size and weight of the radio apparatus80 are comparatively easily reduced. However, in this case, interfacesfor N series of signals (i.e., N interfaces) for each of reception andtransmission are required between the radio apparatus 80 and the digitalapparatus 90. Therefore, when the number N of antenna elements issignificantly large, a significantly large band is required between theradio apparatus 80 and the digital apparatus 90.

Second Processing Arrangement Case

FIG. 3 is an explanatory diagram for describing the second processingarrangement case of the base station 50. In this example, the antennaweight multiplication units 57 and 75, the channel estimation unit 63,and the antenna weight generating unit 65 are arranged in a radioapparatus 80, not in a digital apparatus 90.

In the second processing arrangement case, interfaces for M series ofsignals (i.e., M interfaces) for reception and interfaces for L seriesof signals (i.e., L interfaces) for transmission are only requiredbetween the radio apparatus 80 and the digital apparatus 90. Therefore,even when the number N of antenna elements is significantly large, a notsignificantly large band is required between the radio apparatus 80 andthe digital apparatus 90. However, channel estimation and generation ofantenna weights (especially the latter) are complicated and specialprocessing. Therefore, a circuit scale of the radio apparatus 80 isincreased, which hinders reduction in size and weight of the radioapparatus 80. Further, channel estimation and generation of antennaweights are processing performed for each user (terminal apparatus), andtherefore the radio apparatus 80 is required to perform processing inconsideration of a user (terminal apparatus).

In the light of what has been described above, it is desirable to enableboth a circuit scale of an apparatus (radio apparatus) that receivessignals via antennas and a band of an interface between apparatuses(interface between a radio apparatus and a digital apparatus) to besmall.

2. Overview of Example Embodiments

In example embodiments of the present invention (hereinafter referred toas the present example embodiments), a radio apparatus receives signalsvia a plurality of antennas (e.g., a plurality of antenna elementsincluded in a multi-element antenna). Further, in the present exampleembodiments in particular, the radio apparatus multiplies the signalsreceived via the plurality of antennas by receiving antenna weights.

Moreover, in the present example embodiments in particular, the radioapparatus transmits, to a digital apparatus, channel related informationrelated to a channel of signals received via the plurality of antennas.The digital apparatus receives the channel related information. Then,based on the channel related information, weight information related toreceiving antenna weights is generated. Further, the digital apparatustransmits the weight information to the radio apparatus. The radioapparatus receives the weight information. After that, the radioapparatus multiplies the signals received via the plurality of antennasby the receiving antenna weights.

In this manner, for example, both a circuit scale of the radio apparatusand a band of an interface between the radio apparatus and the digitalapparatus can be small.

Note that the above-described technical features are concrete examplesof the present example embodiments, and it is apparent that the presentexample embodiments are not limited to the above-described technicalfeatures.

3. First Example Embodiment

Next, with reference to FIG. 4 to FIG. 13 , a first example embodimentof the present invention will be described.

<3.1. Configuration of System>

First, with reference to FIG. 4 and FIG. 5 , an example of aconfiguration of a system 1 according to the first example embodimentwill be described. FIG. 4 is an explanatory diagram illustrating anexample of a schematic configuration of the system 1 according to thefirst example embodiment. With reference to FIG. 4 , the system 1includes a base station 10 and a terminal apparatus 40.

For example, the system 1 is a system conforming to Third GenerationPartnership Project (3GPP) standards. More specifically, the system 1may be a system conforming to LTE/LTE-Advanced and/or SystemArchitecture Evolution (SAE). Alternatively, the system 1 may be asystem conforming to fifth generation (5G) standards. Of course, thesystem 1 is not limited to these examples.

(1) Base Station 10

The base station 10 is a node of a radio access network (RAN), andperforms radio communication with a terminal apparatus (e.g., theterminal apparatus 40) located in a coverage area.

Concrete Examples of Base Station 10

The base station 10 is a node that performs radio communication with aterminal apparatus, i.e., a node of a radio access network (RAN). Forexample, the base station 10 may be an evolved Node B (eNB), or may be ageneration Node B (gNB) in 5G. The base station 10 may include aplurality of units (or a plurality of nodes). The plurality of units (orthe plurality of nodes) may include a first unit (or a first node) thatperforms processing of a higher protocol layer, and a second unit (or asecond node) that performs processing of a lower protocol layer. As anexample, the first unit may be referred to as a center/central unit(CU), and the second unit may be referred to as a distributed unit (DU)or an access unit (AU). As another example, the first unit may bereferred to as a digital unit (DU), and the second unit may be referredto as a radio unit (RU) or a remote unit (RU). The digital unit (DU) maybe a base band unit (BBU), and the RU may be a remote radio head (RRH)or a remote radio unit (RRU). The terms for the first unit (or the firstnode) and the second unit (or the second node) are, of course, notlimited to these examples. Alternatively, the base station 10 may be asingle unit (or a single node). In this case, the base station 10 may beone unit (e.g., the second unit) of the plurality of units, and may beconnected to another unit (e.g., the first unit) of the plurality ofunits.

Configuration of Base Station 10

FIG. 5 is an explanatory diagram illustrating an example of a schematicconfiguration of the base station 10 according to the first exampleembodiment. With reference to FIG. 5 , the base station 10 includes adigital apparatus 100, a radio apparatus 200, and a plurality ofantennas 300. For example, the base station 10 includes N antennas 300.

Digital Apparatus 100 and Radio Apparatus 200

Each of the digital apparatus 100 and the radio apparatus 200 is one ofa plurality of apparatuses constituting the base station 10. The basestation 10 may further include another apparatus (not illustrated) otherthan the digital apparatus 100 and the radio apparatus 200 (and theplurality of antennas 300).

The radio apparatus 200 is an apparatus physically separated from thedigital apparatus 100. The radio apparatus 200 is connected to theplurality of antennas 300. The digital apparatus 100 is connected to theradio apparatus 200. The digital apparatus 100 and the radio apparatus200 are connected to each other with a communication line 21. Thedigital apparatus 100 receives information from the radio apparatus 200via the communication line 21, and transmits information to the radioapparatus 200 via the communication line 21. For example, thecommunication line 21 is an optical fiber line. For example, the digitalapparatus 100 is located indoors, and the radio apparatus 200 is locatedoutdoors.

When the base station 10 includes the first unit and the second unit asdescribed above, the digital apparatus 100 may be the first unit (e.g.,a digital unit (DU) or a BBU), and the radio apparatus 200 may be thesecond unit (e.g., a remote/radio unit (RU), an RRH, or an RRU).Alternatively, the digital apparatus 100 and the radio apparatus 200 maybe an apparatus included in the second unit (e.g., a distributed unit(DU)).

Note that the digital apparatus 100 is referred to as a digitalapparatus since the digital apparatus 100 performs processing of digitalsignals. More generally, however, the digital apparatus 100 may bereferred to as a communication apparatus. The radio apparatus 200 isreferred to as a radio apparatus since the radio apparatus 200 performsprocessing of radio signals as in the later description. More generally,however, the radio apparatus 200 may be referred to as a communicationapparatus. Of course, the radio apparatus 200 may perform processing ofdigital signals, as well as processing of radio signals. Here, for thesake of better understanding of the first example embodiment, the terms“digital apparatus” and “radio apparatus” are used, instead of the term“communication apparatus.”

Plurality of Antennas 300

For example, each of the plurality of antennas 300 is an antenna elementincluded in a multi-element antenna. For example, the multi-elementantenna is an antenna for massive multiple-input and multiple-output(massive MIMO).

(2) Terminal Apparatus 40

The terminal apparatus 40 performs radio communication with a basestation. For example, when the terminal apparatus 40 is located in acoverage area of the base station 10, the terminal apparatus 40 performsradio communication with the base station 10. For example, the terminalapparatus 40 may be referred to as a user equipment (UE), a userterminal, or a mobile station.

FIG. 4 illustrates only one terminal apparatus 40. However, of course, aplurality of terminal apparatus 40 may be present.

<3.2. Configuration of Digital Apparatus>

Next, with reference to FIG. 6 , an example of a configuration of thedigital apparatus 100 according to the first example embodiment will bedescribed. FIG. 6 is a block diagram illustrating an example of aschematic configuration of the digital apparatus 100 according to thefirst example embodiment. With reference to FIG. 6 , the digitalapparatus 100 includes an interface 110, a storage unit 120, and aprocessing unit 130.

(1) Interface 110

The interface 110 is an interface for communication with the radioapparatus 200. In other words, the interface 110 is an interface for thecommunication line 21 (e.g., an optical fiber line) that connects thedigital apparatus 100 and the radio apparatus 200. Through the interface110, signals from the radio apparatus 200 are received, and signals tothe radio apparatus 200 are transmitted.

(2) Storage Unit 120

The storage unit 120 temporarily or permanently stores programs(instructions) and parameters for operation of the digital apparatus100, and various pieces of data. The program includes one or moreinstructions for operations of the digital apparatus 100.

(3) Processing Unit 130

The processing unit 130 provides various functions of the digitalapparatus 100. The processing unit 130 includes a radio communicationprocessing unit 131, a reception processing unit 133, a generating unit135, and a transmission processing unit 137. Note that the processingunit 130 may further include another constituent element other thanthese constituent elements. Specifically, the processing unit 130 mayalso perform operation other than operation of these constituentelements. Concrete operations of the radio communication processing unit131, the reception processing unit 133, the generating unit 135, and thetransmission processing unit 137 will be described later in detail.

For example, the processing unit 130 communicates with the radioapparatus 200 via the interface 110.

(4) Implementation Example

The interface 110 may be implemented with a converter (e.g., anoptical/electrical (O/E) converter and/or an electrical/optical (E/O)converter), or the like. The storage unit 120 may be implemented with amemory (e.g., a non-volatile memory and/or a volatile memory) and/or ahard disk, or the like. The processing unit 130 may be implemented withone or more processors, such as a baseband (BB) processor and/or anothertype of processor. The radio communication processing unit 131, thereception processing unit 133, the generating unit 135, and thetransmission processing unit 137 may be implemented with the sameprocessor, or may be implemented with separate processors. The memory(storage unit 120) may be included in the one or more processors, or maybe located outside the one or more processors.

The digital apparatus 100 may include a memory that stores a program(instructions), and one or more processors that can execute the program(instructions). The one or more processors may execute the program toperform operations of the processing unit 130 (operations of the radiocommunication processing unit 131, the reception processing unit 133,the generating unit 135, and/or the transmission processing unit 137).The program may be a program for causing the processor(s) to executeoperations of the processing unit 130 (operations of the radiocommunication processing unit 131, the reception processing unit 133,the generating unit 135, and/or the transmission processing unit 137).

<3.3. Configuration of Radio Apparatus>

Next, with reference to FIG. 7 , an example of a configuration of theradio apparatus 200 according to the first example embodiment will bedescribed. FIG. 7 is a block diagram illustrating an example of aschematic configuration of the radio apparatus 200 according to thefirst example embodiment. With reference to FIG. 7 , the radio apparatus200 includes a first interface 210, a second interface 220, a storageunit 230, and a processing unit 240.

(1) First Interface 210

The first interface 210 is an interface for radio communication via theplurality of antennas 300. The first interface 210 receives radiosignals from the plurality of antennas 300, and transmits radio signalsto the plurality of antennas 300.

(2) Second Interface 220

The second interface 220 is an interface for communication with thedigital apparatus 100. In other words, the second interface 220 is aninterface for the communication line 21 (e.g., an optical fiber line)that connects the digital apparatus 100 and the radio apparatus 200. Thesecond interface 220 receives signals from the digital apparatus 100,and transmits signals to the digital apparatus 100.

(3) Storage Unit 230

The storage unit 230 temporarily or permanently stores programs(instructions) and parameters for operation of the radio apparatus 200,and various pieces of data. The program includes one or moreinstructions for operations of the radio apparatus 200.

(4) Processing Unit 240

The processing unit 240 provides various functions of the radioapparatus 200. The processing unit 240 includes a radio communicationprocessing unit 241, a transmission processing unit 243, and a receptionprocessing unit 245. Note that the processing unit 240 may furtherinclude another constituent element other than these constituentelements. In other words, the processing unit 240 may also performoperations other than the operations of these constituent elements.Concrete operations of the radio communication processing unit 241, thetransmission processing unit 243, and the reception processing unit 245will be described later in detail.

For example, the processing unit 240 communicates with the digitalapparatus 100 via the second interface 220. The processing unit 240(radio communication processing unit 241) transmits and/or receivesradio signals via the first interface 210 (hence, via the plurality ofantennas 300).

(5) Implementation Example

The first interface 210 may be implemented with a radio frequency (RF)circuit and an A/D converter, or the like. The second interface 220 maybe implemented with a converter (e.g., an O/E converter and/or an E/Oconverter), or the like. The storage unit 230 may be implemented with amemory (e.g., a non-volatile memory and/or a volatile memory) and/or ahard disk, and the like. The processing unit 240 may be implemented withone or more processors, such as a BB processor and/or another type ofprocessor. The radio communication processing unit 241, the transmissionprocessing unit 243, and the reception processing unit 245 may beimplemented with the same processor, or may be implemented with separateprocessors. The memory (storage unit 230) may be included in the one ormore processors, or may be located outside the one or more processors.

The radio apparatus 200 may include a memory that stores a program(instructions), and one or more processors that can execute the program(instructions). The one or more processors may execute the program toperform operations of the processing unit 240 (operations of the radiocommunication processing unit 241, the transmission processing unit 243,and/or the reception processing unit 245). The program may be a programfor causing the processor(s) to execute operations of the processingunit 240 (operations of the radio communication processing unit 241, thetransmission processing unit 243, and/or the reception processing unit245).

<3.4. Technical Features>

Next, with reference to FIG. 8 to FIG. 14 , technical features of thefirst example embodiment will be described.

(1) Radio Communication Processing

Reception Processing

The radio apparatus 200 (first interface 210 and radio communicationprocessing unit 241) receives signals via the plurality of antennas 300.Further, in the first example embodiment in particular, the radioapparatus 200 (radio communication processing unit 241) multiplies thesignals received via the plurality of antennas 300 by receiving antennaweights. For example, the receiving antenna weights may also be referredto as (receive) beamforming weights (i.e., weights used on a receptionside to perform beamforming).

For example, the digital apparatus 100 (radio communication processingunit 131) performs demodulation and decoding for signals of one or morelayers generated by the radio apparatus 200 multiplying the signalsreceived via the plurality of antennas 300 by the receiving antennaweights.

With reference to FIG. 8 , an example of reception processing of thedigital apparatus 100 and the radio apparatus 200 will be described.FIG. 8 is an explanatory diagram for describing a schematic example ofradio communication processing of the first example embodiment.

The radio apparatus 200 (transmission and/or reception unit 401)converts radio received signals (N series of radio received signals) ofthe plurality of antennas 300 (N antennas 300) into N series ofreception baseband signals on a time axis. Then, the radio apparatus 200(FFT unit 403) converts the N series of reception baseband signals on atime axis into N series of received signals on a frequency axis, bymeans of FFT. Further, the radio apparatus 200 (antenna weightmultiplication unit 405) multiplies the N series of received signals ona frequency axis by a receiving antenna weight matrix having M rows andN columns (a vector if M is 1). As a result, M series of receivedsignals (i.e., received signals of M layers) are output, to betransmitted to the digital apparatus 100.

For example, as described above, signals to be transmitted from theradio apparatus 200 to the digital apparatus 100 are not N series ofreceived signals, but are M series of received signals (received signalsof M layers). Therefore, even when the number N of antennas isincreased, a band of an interface between the digital apparatus 100 andthe radio apparatus 200 can be small.

The digital apparatus 100 (demodulation unit 407 and decoding unit 409)demodulates the M series of received signals (i.e., received signals ofM layers), and decodes the demodulated received signals. For example,decoded information is transmitted from the digital apparatus 100 toanother apparatus, and is to be processed by such another apparatus.Alternatively, decoded information may be further processed by thedigital apparatus 100.

Note that, for example, the transmission and/or reception unit 401 ofFIG. 8 is included in the first interface 210 of FIG. 7 , and the FFTunit 403 and the antenna weight multiplication unit 405 of FIG. 8 areincluded in the radio communication processing unit 241 of FIG. 7 . Forexample, the demodulation unit 407 and the decoding unit 409 of FIG. 8are included in the radio communication processing unit 131 of FIG. 6 .

For example, as described above, the digital apparatus 100 and the radioapparatus 200 perform reception processing of a physical layer (alsoreferred to as layer 1). Specifically, the radio apparatus 200 performsa part of reception processing of the physical layer, and the digitalapparatus 100 performs the rest of reception processing of the physicallayer.

Transmission Processing

For example, the digital apparatus 100 (radio communication processingunit 131) performs coding and modulation to generate signals of one ormore layers.

For example, in the first example embodiment in particular, the radioapparatus 200 (radio communication processing unit 241) multiplies thesignals of one or more layers by the transmitting antenna weights.Further, the radio apparatus 200 (first interface 210 and radiocommunication processing unit 241) transmits the signals generated bybeing multiplied by the transmitting antenna weights, via the pluralityof antennas 300. For example, the transmitting antenna weights may alsobe referred to as (transmit) beamforming weights (i.e., weights used ona transmission side to perform beamforming).

With reference to FIG. 8 again, the digital apparatus 100 (coding unit421 and modulation unit 423) codes transmission signals, and modulatesthe coded transmission signals. As a result, L series of transmissionsignals (transmission signals of L layers) are output, to be transmittedto the radio apparatus 200.

The radio apparatus 200 (antenna weight multiplication unit 425)multiplies the L series of transmission signals by a transmittingantenna weight matrix having N rows and L columns, to thereby generate Nseries of transmission signals on a frequency axis. Then, the radioapparatus 200 (IFFT unit 427) converts the N series of transmissionsignals on a frequency axis into N series of baseband signals on a timeaxis, by means of IFFT. Further, the radio apparatus 200 (transmissionand/or reception unit 401) converts the N series of baseband signals ona time axis into N series of radio transmission signals. Then, the Nseries of radio transmission signals are transmitted from the pluralityof antennas 300 (N antennas 300).

For example, as described above, signals to be transmitted from thedigital apparatus 100 to the radio apparatus 200 are not N series ofreceived signals, but are L series of received signals (received signalsof L layers). Therefore, even when the number N of antennas isincreased, a band of an interface between the digital apparatus 100 andthe radio apparatus 200 can be small.

Note that, for example, the coding unit 421 and the modulation unit 423of FIG. 8 are included in the radio communication processing unit 131 ofFIG. 6 . For example, the antenna weight multiplication unit 425 and theIFFT unit 427 of FIG. 8 are included in the radio communicationprocessing unit 241 of FIG. 7 , and the transmission and/or receptionunit 401 of FIG. 8 is included in the first interface 210 of FIG. 7 .

For example, as described above, the digital apparatus 100 and the radioapparatus 200 perform transmission processing of a physical layer (alsoreferred to as layer 1). Specifically, the radio apparatus 200 performsa part of transmission processing of the physical layer, and the digitalapparatus 100 performs the rest of transmission processing of thephysical layer.

(2) Receiving Antenna Weights

In the first example embodiment in particular, the radio apparatus 200(transmission processing unit 243) transmits, to the digital apparatus100, channel related information related to a channel of signalsreceived via the plurality of antennas 300. The digital apparatus 100(reception processing unit 133) receives the channel related informationfrom the radio apparatus 200.

For example, the digital apparatus 100 (generating unit 135) generatesweight information related to receiving antenna weights, based on thechannel related information.

Further, the digital apparatus 100 (transmission processing unit 137)transmits the weight information to the radio apparatus 200. The radioapparatus 200 (reception processing unit 245) receives the weightinformation from the digital apparatus 100.

After that, the radio apparatus 200 (radio communication processing unit241) multiplies the signals received via the plurality of antennas 300by the receiving antenna weights.

(2-1) Signal

The signals received via the plurality of antennas 300 are uplinksignals (i.e., signals transmitted from the terminal apparatus 40 to thebase station 10).

(2-2) Channel Related Information

Channel

For example, the channel is a channel between the terminal apparatus 40and the plurality of antennas 300.

First Example: Reference Signal

For example, the channel related information is reference signalsreceived via the plurality of antennas 300. Specifically, the radioapparatus 200 (transmission processing unit 243) transmits the referencesignals to the digital apparatus 100. The reference signals areinformation to be used for channel estimation of the channel.

In this case, the digital apparatus 100 (generating unit 135) performschannel estimation, based on the reference signals to calculate channelestimates. Then, the digital apparatus 100 (generating unit 135)generates the weight information, based on the channel estimates.

With reference to FIG. 9 , a first example of channel estimation andweight information generation will be described. FIG. 9 is anexplanatory diagram for describing a first example of channel estimationand weight information generation of the first example embodiment. Withreference to FIG. 9 , the radio apparatus 200 (transmission processingunit 243) transmits reference signals (N series of reference signals) ofan output (N series of received signals on a frequency axis) of the FFTunit 403 to the digital apparatus 100. The digital apparatus 100(reception processing unit 133) receives the reference signals. Then,the digital apparatus 100 (channel estimation unit 411: generating unit135) performs channel estimation, based on the reference signals tocalculate channel estimates (N series of channel estimates). Further,the digital apparatus 100 (antenna weight generating unit 413:generating unit 135) calculates receiving antenna weights (receivingantenna weight matrix having M rows and N columns), based on the channelestimates to generate weight information related to the receivingantenna weights. The digital apparatus 100 (transmission processing unit137) transmits the weight information to the radio apparatus 200. Theradio apparatus 200 (reception processing unit 245) receives the weightinformation. After that, the radio apparatus 200 (radio communicationprocessing unit 241) sets the receiving antenna weights as weights to beused to multiply the signals received via the plurality of antennas 300.This configuration allows the radio apparatus 200 (radio communicationprocessing unit 241) to multiply the signals received via the pluralityof antennas 300 by the receiving antenna weights.

According to this example, neither the channel estimation unit 411 northe antenna weight generating unit 413 is included in the radioapparatus 200, but both the channel estimation unit 411 and the antennaweight generating unit 413 are included in the digital apparatus 100.Therefore, a circuit scale of the radio apparatus 200 can be furtherreduced.

For example, the reference signals are reference signals transmittedduring a specific period in a time frame. FIG. 10 is an explanatorydiagram for describing an example of the reference signals of the firstexample embodiment. With reference to FIG. 10 , one of repeated timeframes 1001, and a specific period 1003 in one time frame 1001 areillustrated. For example, reference signals 1011 are transmitted in thespecific period 1003. For example, a signal pattern of the referencesignals 1011 is constant in the entire band, and thus each user (eachterminal apparatus) transmits reference signals in an allocated band ofthe entire band. For example, this configuration facilitatestransmission of reference signals from the radio apparatus 200 to thedigital apparatus 100. More specifically, for example, even if the radioapparatus 200 does not hold information for each user (terminalapparatus), the radio apparatus 200 can extract only reference signalsout of received signals, and can transmit the reference signals to thedigital apparatus 100. Note that the specific period 1003 is located atthe end of the time frame 1001 as illustrated in FIG. 10 , for example.However, location of the specific period 1003 is not limited to thisexample. For example, the specific period 1003 may be located at thebeginning of the time frame 1001, or may be located at a position otherthan the beginning and the end of the time frame 1001. The specificperiod 1003 may be one continuous period as illustrated in FIG. 10 , ormay be two or more distributed periods.

As an example, the time frame is a radio frame, and the specific periodis a specific symbol. Specifically, the reference signals aretransmitted in a specific symbol in a radio frame. Note that, forexample, one radio frame includes a predetermined number of subframes,and one subframe includes a predetermined number of symbols. Note thatthe time frame and the specific period are not limited to this example.

For example, the reference signals are sounding reference signals (SRS).Alternatively, the reference signals may be demodulation referencesignals (DMRS).

Note that the base station 10 (digital apparatus 100 and radio apparatus200) may perform communication in time division duplex (TDD). In thiscase, for example, as illustrated in FIG. 11 , the reference signals1011 may be transmitted from the radio apparatus 200 to the digitalapparatus 100. Specifically, the radio apparatus 200 receives referencesignals 1011 and other signals 1013 (such as data signals and controlsignals) as radio received signals in a reception period 1021 (i.e., anuplink period), whereas the radio apparatus 200 does not receive signalsin a transmission period 1023 (i.e., a downlink period). Therefore, asillustrated in FIG. 11 , for example, the radio apparatus 200 maytransmit such other signals (M series of signals) to the digitalapparatus 100 in the reception period 1021, and may transmit thereference signals (N series of signals) to the digital apparatus 100 inthe subsequent transmission period 1023 (and a part of the receptionperiod 1021).

Second Example: Channel Estimates

The channel related information may be channel estimates which the radioapparatus 200 calculates by channel estimation based on referencesignals received via the plurality of antennas 300. Specifically, theradio apparatus 200 may perform channel estimation, based on thereference signals to calculate channel estimates, and transmit thechannel estimates to the digital apparatus 100.

With reference to FIG. 12 , a second example of channel estimation andweight information generation will be described. FIG. 12 is anexplanatory diagram for describing a second example of channelestimation and weight information generation of the first exampleembodiment. With reference to FIG. 12 , the radio apparatus 200 (channelestimation unit 411: radio communication processing unit 241) performschannel estimation, based on reference signals (N series of referencesignals) of an output (N series of received signals on a frequency axis)of the FFT unit 403 to calculate channel estimates (N series of channelestimates). Then, the radio apparatus 200 (transmission processing unit243) transmits the channel estimates to the digital apparatus 100. Thedigital apparatus 100 (reception processing unit 133) receives thechannel estimates. Further, the digital apparatus 100 (antenna weightgenerating unit 413: generating unit 135) calculates receiving antennaweights (receiving antenna weight matrix having M rows and N columns),based on the channel estimates to generate weight information related tothe receiving antenna weights. The subsequent processing is the same asthe processing of the example of FIG. 9 , and hence overlappingdescription thereof is herein omitted.

According to this example, what is to be transmitted from the radioapparatus 200 to the digital apparatus 100 is not reference signalsthemselves, but is channel estimates. For example, an amount of data ofchannel estimates may be compressed by averaging of channel estimates ona frequency axis or the like. Therefore, a band of an interface betweenthe radio apparatus 200 and the digital apparatus 100 can be furthersmall.

(2-3) Weight Information

As described above, the weight information is weight information relatedto the receiving antenna weights. For example, the weight information isinformation indicating the receiving antenna weights.

Moreover, as described above, the receiving antenna weights are weightsby which the radio apparatus 200 multiplies signals received via theplurality of antennas 300. For example, the receiving antenna weightsare weights by which the radio apparatus 200 multiplies signals from theterminal apparatus 40, the signals being received via the plurality ofantennas.

For example, as described above, the receiving antenna weights are areceiving antenna weight matrix having M rows and N columns (a vector ifM is 1). In this case, the weight information is information indicatingthe receiving antenna weight matrix having M rows and N columns.

As a first example, the weight information includes informationindicating respective weights included in the receiving antenna weights.Specifically, for example, the receiving antenna weights are a receivingantenna weight matrix having M rows and N columns, and the weightinformation includes information indicating respective elements(weights) included in the receiving antenna weight matrix. Specifically,the weight information includes information indicating respective M×Nelements. For example, this configuration enables more flexible settingof receiving antenna weights.

As a second example, the receiving antenna weights may be one receivingantenna weight set included in a plurality of predetermined receivingantenna weight sets, and the weight information may be an indexindicating the one receiving antenna weight set. Specifically, forexample, a plurality of receiving antenna weight sets and an indexindicating each of the plurality of receiving antenna weight sets may bedefined as a codebook in advance, and the weight information may be anindex indicating one receiving antenna weight set in the codebook. Thisconfiguration further reduces an amount of information of weightinformation, for example.

(2-4) Information Related to Use of Receiving Antenna Weights

For example, the digital apparatus 100 (transmission processing unit137) transmits, to the radio apparatus 200, the weight information andinformation related to use of the receiving antenna weights (hereinafterreferred to as “use information”). This configuration enables the radioapparatus 200 to actually perform multiplication of the receivingantenna weights, for example.

Frequency Information

For example, the use information includes frequency information relatedto frequencies for which the receiving antenna weights are used. Forexample, the frequencies for which the receiving antenna weights areused are frequencies allocated to the terminal apparatus 40.Specifically, the frequency information is information related tofrequencies allocated to the terminal apparatus 40.

For example, the frequency information indicates a frequency block forwhich the receiving antenna weights are used, out of a plurality offrequency blocks. In other words, the frequency information indicates afrequency block in which signals to be multiplied by the plurality ofantenna weights are transmitted. The frequency information may indicateone frequency block, or may indicate a plurality of frequency blocks.For example, the frequency block is a resource block (or a resourceblock group).

Further, or alternatively, the frequency information may indicate afrequency resolution of the receiving antenna weights. In other words,the frequency information may indicate a width (unit width) of thefrequencies for which the receiving antenna weights are used.

Such frequency information as described above allows the radio apparatus200 to be notified of which signals the radio apparatus 200 needs tomultiply by the receiving antenna weights, and frequencies in which thesignals are transmitted, for example.

Time Information

For example, the use information includes time information related totime when the receiving antenna weights are used. For example, the timewhen the receiving antenna weights are used is time allocated to theterminal apparatus 40. Specifically, the time information is informationrelated to time allocated to the terminal apparatus 40.

For example, the time information indicates a period in which thereceiving antenna weights are used. In other words, the time informationindicates a period in which signals to be multiplied by the plurality ofantenna weights are transmitted. The period may be a subframe, or may bea slot. However, the period is not limited to these examples.

Such time information as described above allows the radio apparatus 200to be notified of which signals the radio apparatus 200 needs tomultiply by the receiving antenna weights, and time when the signals aretransmitted, for example.

The frequency information and the time information may be radio resourceinformation (which may also be referred to as resource allocationinformation or scheduling information) related to radio resources inwhich the receiving antenna weights are used.

As described above, the radio apparatus 200 transmits the channelrelated information to the digital apparatus 100. The digital apparatus100 generates the weight information related to the receiving antennaweights, based on the channel related information, and transmits theweight information to the radio apparatus 200. Then, the radio apparatus200 multiplies the signals received via the plurality of antennas 300 bythe receiving antenna weights. In this manner, generation of the weightinformation (calculation of the receiving antenna weights) is performedby the digital apparatus 100, not by the radio apparatus 200. Therefore,a circuit scale of the radio apparatus 200 can be small.

(3) Flow of Processing

Radio Communication Processing

With reference to FIG. 13 , an example of radio communication processingaccording to the first example embodiment will be described. FIG. 13 isa sequence diagram for describing an example of a schematic flow ofradio communication processing according to the first exampleembodiment.

The radio apparatus 200 receives signals via the plurality of antennas300 (S501).

The radio apparatus 200 multiplies the signals received via theplurality of antennas 300 by receiving antenna weights (S503). In thismanner, for example, signals of one or more layers are generated.

The radio apparatus 200 transmits the signals of one or more layers tothe digital apparatus 100 (S505).

The digital apparatus 100 performs demodulation and decoding for thesignals of one or more layers (S507).

Transmission and/or Reception of Channel Related Information and WeightInformation

With reference to FIG. 14 , an example of processing of transmissionand/or reception of channel related information and weight informationaccording to the first example embodiment will be described. FIG. 14 isa sequence diagram for describing an example of a schematic flow ofprocessing of transmission and/or reception of channel relatedinformation and weight information according to the first exampleembodiment.

The radio apparatus 200 receives signals via the plurality of antennas300 (S521).

The radio apparatus 200 transmits channel related information related toa channel of the signals received via the plurality of antennas 300 tothe digital apparatus 100, and the digital apparatus 100 receives thechannel related information (S523).

The digital apparatus 100 generates weight information related toreceiving antenna weights, based on the channel related information(S525).

The digital apparatus 100 transmits the weight information to the radioapparatus 200, and the radio apparatus 200 receives the weightinformation (S527).

The radio apparatus 200 sets the receiving antenna weights as weights tobe used to multiply signals received via the plurality of antennas 300(S529).

<3.5. Example Alteration>

As described above, in the first example embodiment, the digitalapparatus 100 (transmission processing unit 137) transmits, to the radioapparatus 200, weight information related to receiving antenna weightsby which the radio apparatus 200 multiplies signals received via theplurality of antennas 300. The radio apparatus 200 (reception processingunit 245) receives the weight information from the digital apparatus100.

First Example

In an example alteration of the first example embodiment, for example,the digital apparatus 100 (transmission processing unit 137) may alsotransmit, to the radio apparatus 200, other weight information relatedto transmitting antenna weights which the radio apparatus 200 uses forgeneration of signals to be transmitted via the plurality of antennas300. Then, the radio apparatus 200 (reception processing unit 245) mayreceive such other weight information from the digital apparatus 100.For example, the digital apparatus 100 (generating unit 135) maygenerate such other weight information, based on the channel relatedinformation.

The transmitting antenna weights may be a transmitting antenna weightmatrix having N rows and L columns (a vector if L is 1).

Such other weight information related to the transmitting antennaweights may be information in a format the same as a format of theweight information related to the receiving antenna weights.

The radio apparatus 200 (radio communication processing unit 241) mayset the transmitting antenna weights, based on such other weightinformation. Then, the radio apparatus 200 (radio communicationprocessing unit 241) may multiply signals of one or more layers (e.g.,signals of L layers) by the transmitting antenna weights, to therebygenerate signals to be transmitted via the plurality of antennas 300.

Second Example

Alternatively, the receiving antenna weights may be antenna weightswhich the radio apparatus 200 also uses for generation of signals to betransmitted via the plurality of antennas. Specifically, the receivingantenna weights and the transmitting antenna weights may be the same.For example, when the number L of transmission layers and the number Mof reception layers are the same, the receiving antenna weights and thetransmitting antenna weights may be the same, as described above.

Regardless of the first example or the second example, in a firstexample alteration in particular, the base station 10 (digital apparatus100 and radio apparatus 200) may perform communication in TDD.

The first example embodiment has been described above. According to thefirst example embodiment, both a circuit scale of the radio apparatus200 and a band of an interface between the radio apparatus 200 and thedigital apparatus 100 can be small.

4. Second Example Embodiment

Next, with reference to FIG. 15 to FIG. 17 , a second example embodimentof the present invention will be described. The above-described firstexample embodiment is a concrete example embodiment, whereas the secondexample embodiment is a more generalized example embodiment.

<4.1. Configuration of System>

First, with reference to FIG. 15 , an example of a configuration of asystem 2 according to the second example embodiment will be described.FIG. 15 is an explanatory diagram illustrating an example of a schematicconfiguration of the system 2 according to the second exampleembodiment. With reference to FIG. 15 , the system 2 includes a firstcommunication apparatus 600, a second communication apparatus 700, and aplurality of antennas 800.

For example, the system 2 is a base station. For example, descriptionconcerning the base station is the same as the description concerningthe base station 10 of the first example embodiment. Hence, overlappingdescription thereof is herein omitted.

First Communication Apparatus 600 and Second Communication Apparatus 700

For example, each of the first communication apparatus 600 and thesecond communication apparatus 700 is one of a plurality of apparatusesconstituting a base station. The system 2 (base station) may furtherinclude another apparatus (not illustrated) other than the firstcommunication apparatus 600 and the second communication apparatus 700(and the plurality of antennas 800).

The second communication apparatus 700 is an apparatus physicallyseparated from the first communication apparatus 600. For example, thesecond communication apparatus 700 is connected to the plurality ofantennas 800. The first communication apparatus 600 is connected to thesecond communication apparatus 700. For example, the first communicationapparatus 600 and the second communication apparatus 700 are connectedto each other with a communication line 23. The first communicationapparatus 600 receives information from the second communicationapparatus 700 via the communication line 23, and transmits informationto the second communication apparatus 700 via the communication line 23.For example, the communication line 23 is an optical fiber line (opticalfiber cable). Further, for example, the first communication apparatus600 is located indoors, and the second communication apparatus 700 islocated outdoors.

When the base station (system 2) includes the first unit and the secondunit (refer to the first example embodiment), the first communicationapparatus 600 may be the first unit (e.g., a digital unit (DU) or aBBU), and the second communication apparatus 700 may be the second unit(e.g., a remote/radio unit (RU), an RRH, or an RRU). Alternatively, thefirst communication apparatus 600 and the second communication apparatus700 may be apparatuses included in the second unit (e.g., a distributedunit (DU)).

Plurality of Antennas 800

For example, each of the plurality of antennas 800 is an antenna elementincluded in a multi-element antenna. For example, the multi-elementantenna is an antenna for massive MIMO.

The configuration of the system 2 has been described above. As anexample, the first communication apparatus 600 may be the digitalapparatus 100 of the first example embodiment. The second communicationapparatus 700 may be the radio apparatus 200 of the first exampleembodiment. The plurality of antennas 800 may be the plurality ofantennas 300 of the first example embodiment. Of course, the secondexample embodiment is not limited to this example. As an example, thefirst communication apparatus 600 may be an apparatus (a component or amodule) included in the digital apparatus 100 of the first exampleembodiment, and the second communication apparatus 700 may be anapparatus (a component or a module) included in the radio apparatus 200of the first example embodiment. As another example, the firstcommunication apparatus 600 may be a third apparatus that is differentfrom a digital apparatus, while the second communication apparatus 700is a radio apparatus.

<4.2. Configuration of First Communication Apparatus>

Next, with reference to FIG. 16 , an example of a configuration of thefirst communication apparatus 600 according to the second exampleembodiment will be described. FIG. 16 is a block diagram illustrating anexample of a schematic configuration of the first communicationapparatus 600 according to the second example embodiment. With referenceto FIG. 16 , the first communication apparatus 600 includes a receptionprocessing unit 610 and a transmission processing unit 620.

Concrete operations of the reception processing unit 610 and thetransmission processing unit 620 will be described later.

The reception processing unit 610 and the transmission processing unit620 may be implemented with one or more processors (such as a BBprocessor and/or another type of processor) and a memory.

The first communication apparatus 600 may include a memory that stores aprogram (instructions), and one or more processors that can execute theprogram (instructions). The one or more processors may execute theprogram to perform operations of the reception processing unit 610 andthe transmission processing unit 620. The program may be a program forcausing the processor(s) to execute operations of the receptionprocessing unit 610 and the transmission processing unit 620.

Note that, of course, the first communication apparatus 600 may furtherinclude a constituent element other than the reception processing unit610 and the transmission processing unit 620. For example, the firstcommunication apparatus 600 may further include a constituent element(e.g., the interface 110, the storage unit 120, the radio communicationprocessing unit 131, and/or the generating unit 135) included in thedigital apparatus 100 of the first example embodiment.

<4.3. Configuration of Second Communication Apparatus>

Next, with reference to FIG. 17 , an example of a configuration of thesecond communication apparatus 700 according to the second exampleembodiment will be described. FIG. 17 is a block diagram illustrating anexample of a schematic configuration of the second communicationapparatus 700 according to the second example embodiment. With referenceto FIG. 17 , the second communication apparatus 700 includes a radiocommunication processing unit 710, a transmission processing unit 720,and a reception processing unit 730.

Concrete operations of the radio communication processing unit 710, thetransmission processing unit 720, and the reception processing unit 730will be described later.

The radio communication processing unit 710, the transmission processingunit 720, and the reception processing unit 730 may be implemented withone or more processors (such as a BB processor and/or another type ofprocessor) and a memory.

The second communication apparatus 700 may include a memory that storesa program (instructions), and one or more processors that can executethe program (instructions). The one or more processors may execute theprogram to perform operations of the radio communication processing unit710, the transmission processing unit 720, and the reception processingunit 730. The program may be a program for causing the processor(s) toexecute operations of the radio communication processing unit 710, thetransmission processing unit 720, and the reception processing unit 730.

Note that, of course, the second communication apparatus 700 may furtherinclude a constituent element other than the radio communicationprocessing unit 710, the transmission processing unit 720, and thereception processing unit 730. For example, the second communicationapparatus 700 may further include a constituent element (e.g., the firstinterface 210, the second interface 220, and/or the storage unit 230)included in the radio apparatus 200 of the first example embodiment.

<4.4. Technical Features>

Next, technical features of the second example embodiment will bedescribed.

(1) Radio Communication Processing

The second communication apparatus 700 (radio communication processingunit 710) receives signals via the plurality of antennas 800. Further,in the second example embodiment in particular, the second communicationapparatus 700 (radio communication processing unit 710) multiplies thesignals received via the plurality of antennas 800 by receiving antennaweights.

For example, description concerning such radio communication processing(reception processing) is similar to the description of the radiocommunication processing (reception processing) of the first exampleembodiment. Further, description concerning transmission processing mayalso be similar to the description of the transmission processing of thefirst example embodiment. In this case, the second communicationapparatus 700 (radio communication processing unit 710) may operatesimilarly to the radio apparatus 200 (radio communication processingunit 241) of the first example embodiment. The first communicationapparatus 600 may operate similarly to the digital apparatus 100 (radiocommunication processing unit 131) of the first example embodiment.Hence, overlapping description thereof is herein omitted.

Note that, of course, the second example embodiment is not limited tothe example described above. As an example, another apparatus (digitalapparatus) that is not the first communication apparatus 600 may performradio communication processing.

(2) Receiving Antenna Weights

In the second example embodiment in particular, the second communicationapparatus 700 (transmission processing unit 720) transmits, to the firstcommunication apparatus 600, channel related information related to achannel of signals received via the plurality of antennas 800. The firstcommunication apparatus 600 (reception processing unit 610) receives thechannel related information from the second communication apparatus 700.

Based on the channel related information, weight information related toreceiving antenna weights is generated.

Further, the first communication apparatus 600 (transmission processingunit 620) transmits the weight information to the second communicationapparatus 700. The second communication apparatus 700 (receptionprocessing unit 730) receives the weight information from the firstcommunication apparatus 600.

After that, the second communication apparatus 700 (radio communicationprocessing unit 710) multiplies the signals received via the pluralityof antennas 800 by the receiving antenna weights.

For example, description concerning such receiving antenna weights issimilar to the description concerning the receiving antenna weights ofthe first example embodiment. In this case, the second communicationapparatus 700 (radio communication processing unit 710, transmissionprocessing unit 720, and reception processing unit 730) may operatesimilarly to the radio apparatus 200 (radio communication processingunit 241, transmission processing unit 243, reception processing unit245) of the first example embodiment. The first communication apparatus600 (reception processing unit 610 and transmission processing unit 620)may operate similarly to the digital apparatus 100 (reception processingunit 133 and transmission processing unit 137) of the first exampleembodiment. Hence, overlapping description thereof is herein omitted.

Note that, of course, the second example embodiment is not limited tothe example described above. As an example, another apparatus that isnot the first communication apparatus 600 may generate the weightinformation, based on the channel related information.

(3) Flow of Processing

As an example, processing of the second example embodiment is the sameas the processing of the first example embodiment. Hence, overlappingdescription thereof is herein omitted. Note that, of course, the secondexample embodiment is not limited to this example.

The second example embodiment has been described above. According to thesecond example embodiment, both a circuit scale of the secondcommunication apparatus 700 and a band of an interface between thesecond communication apparatus 700 and another communication apparatus(e.g., the first communication apparatus 600) can be small. Note thatthe first example alteration of the first example embodiment may also beapplied to the second example embodiment.

Descriptions have been given above of the example embodiments of thepresent invention. However, the present invention is not limited tothese example embodiments. It should be understood by those of ordinaryskill in the art that these example embodiments are merely examples andthat various alterations are possible without departing from the scopeand the spirit of the present invention.

For example, the steps in the processing described in the Specificationmay not be necessarily performed in the order described in thecorresponding sequence diagram in time series. For example, the steps inthe processing may be performed in an order different from the orderdescribed in the sequence diagram or in parallel. In addition, some ofthe steps in the processing may be deleted, or more steps may be addedto the processing.

Methods including operations or processing of a communication apparatus(digital apparatus, radio apparatus, first communication apparatus, orsecond communication apparatus) described in the Specification may beprovided, and programs for causing a processor to execute the operationsor processing may be provided. Moreover, non-transitorycomputer-readable recording media (non-transitory computer readablemedium) in which the programs are recorded thereon may be provided. Itis apparent that such methods, programs, and non-transitory computerreadable recording media are also included in the present invention.

The whole or part of the example embodiments disclosed above can bedescribed as, but not limited to, the following supplementary notes.

(Supplementary Note 1)

A first communication apparatus comprising:

a reception processing unit configured to receive, from a secondcommunication apparatus which receives signals via a plurality ofantennas, channel related information related to a channel of signalsreceived via the plurality of antennas; and

a transmission processing unit configured to transmit, to the secondcommunication apparatus, weight information related to receiving antennaweights by which the second communication apparatus multiplies signalsreceived via the plurality of antennas, the weight information beinggenerated based on the channel related information.

(Supplementary Note 2)

The first communication apparatus according to Supplementary Note 1,wherein the weight information is information indicating the receivingantenna weights.

(Supplementary Note 3)

The first communication apparatus according to Supplementary Note 2,wherein the weight information includes information indicatingrespective weights included in the receiving antenna weights.

(Supplementary Note 4)

The first communication apparatus according to Supplementary Note 2,wherein

the receiving antenna weights are one receiving antenna weight setincluded in a plurality of predetermined receiving antenna weight sets,and

the weight information is an index indicating the one receiving antennaweight set.

(Supplementary Note 5)

The first communication apparatus according to any one of SupplementaryNotes 1 to 4, wherein the transmission processing unit is configured totransmit, to the second communication apparatus, the weight informationand information related to use of the receiving antenna weights.

(Supplementary Note 6)

The first communication apparatus according to Supplementary Note 5,wherein the information related to use of the receiving antenna weightsincludes frequency information related to frequencies for which thereceiving antenna weights are used.

(Supplementary Note 7)

The first communication apparatus according to Supplementary Note 6,wherein the frequency information indicates a frequency block for whichthe receiving antenna weights are used, out of a plurality of frequencyblocks.

(Supplementary Note 8)

The first communication apparatus according to Supplementary Note 6 or7, wherein the frequency information indicates a frequency resolution ofthe receiving antenna weights.

(Supplementary Note 9)

The first communication apparatus according to any one of SupplementaryNotes 6 to 8, wherein

the channel is a channel between a terminal apparatus and the pluralityof antennas,

the receiving antenna weights are weights by which the secondcommunication apparatus multiplies signals from the terminal apparatus,the signals being received via the plurality of antennas, and

the frequency information is information related to frequenciesallocated to the terminal apparatus.

(Supplementary Note 10)

The first communication apparatus according to Supplementary Note 5,wherein the information related to use of the receiving antenna weightsincludes time information related to time when the receiving antennaweights are used.

(Supplementary Note 11)

The first communication apparatus according to Supplementary Note 10,wherein

the channel is a channel between a terminal apparatus and the pluralityof antennas,

the receiving antenna weights are weights by which the secondcommunication apparatus multiplies signals from the terminal apparatus,the signals being received via the plurality of antennas, and

the time information is information related to time allocated to theterminal apparatus.

(Supplementary Note 12)

The first communication apparatus according to any one of SupplementaryNotes 1 to 11, wherein the channel related information is referencesignals received via the plurality of antennas.

(Supplementary Note 13)

The first communication apparatus according to any one of SupplementaryNotes 1 to 12, wherein the channel related information is channelestimates which the second communication apparatus calculates by channelestimation based on reference signals received via the plurality ofantennas.

(Supplementary Note 14)

The first communication apparatus according to Supplementary Note 12 or13, wherein the reference signals are reference signals transmittedduring a specific period in a time frame.

(Supplementary Note 15)

The first communication apparatus according to Supplementary Note 14,wherein

the time frame is a radio frame, and

the specific period is a specific symbol.

(Supplementary Note 16)

The first communication apparatus according to any one of SupplementaryNotes 12 to 15, wherein the reference signals are sounding referencesignals (SRS) or demodulation reference signals (DMRS).

(Supplementary Note 17)

The first communication apparatus according to any one of SupplementaryNotes 1 to 16, further comprising a generating unit configured togenerate the weight information based on the channel relatedinformation.

(Supplementary Note 18)

The first communication apparatus according to any one of SupplementaryNotes 1 to 17, further comprising a radio communication processing unitconfigured to perform demodulation and decoding for signals of one ormore layers generated by the second communication apparatus multiplyingsignals received via the plurality of antennas by the receiving antennaweights.

(Supplementary Note 19)

The first communication apparatus according to any one of SupplementaryNotes 1 to 18, wherein the transmission processing unit is configured totransmit, to the second communication apparatus, other weightinformation related to transmitting antenna weights which the secondcommunication apparatus uses for generation of signals to be transmittedvia the plurality of antennas, the other weight information beinggenerated based on the channel related information.

(Supplementary Note 20)

The first communication apparatus according to any one of SupplementaryNotes 1 to 18, wherein the receiving antenna weights are antenna weightswhich the second communication apparatus also uses for generation ofsignals to be transmitted via the plurality of antennas.

(Supplementary Note 21)

The first communication apparatus according to Supplementary Note 19 or20, wherein the second communication apparatus is an apparatus whichperforms communication in time division duplex (TDD).

(Supplementary Note 22)

The first communication apparatus according to any one of SupplementaryNotes 1 to 21, wherein the signals are uplink signals.

(Supplementary Note 23)

The first communication apparatus according to any one of SupplementaryNotes 1 to 22, wherein each of the first communication apparatus and thesecond communication apparatus is one of a plurality of apparatusesconstituting a base station.

(Supplementary Note 24)

The first communication apparatus according to any one of SupplementaryNotes 1 to 23, wherein

the channel is a channel between a terminal apparatus and the pluralityof antennas, and the receiving antenna weights are weights by which thesecond communication apparatus multiplies signals from the terminalapparatus, the signals being received via the plurality of antennas.

(Supplementary Note 25)

The first communication apparatus according to any one of SupplementaryNotes 1 to 24, wherein each of the plurality of antennas is an antennaelement included in a multi-element antenna.

(Supplementary Note 26)

The first communication apparatus according to Supplementary Note 25,wherein the multi-element antenna is an antenna for massivemultiple-input and multiple-output (MIMO).

(Supplementary Note 27)

The first communication apparatus according to any one of SupplementaryNotes 1 to 26, wherein

the transmission processing unit is configured to receive the channelrelated information from the second communication apparatus via acommunication line, and

the reception processing unit is configured to transmit the weightinformation to the second communication apparatus via the communicationline.

(Supplementary Note 28)

The first communication apparatus according to Supplementary Note 27,wherein the communication line is an optical fiber line.

(Supplementary Note 29)

The first communication apparatus according to any one of SupplementaryNotes 1 to 28, wherein the second communication apparatus is anapparatus physically separated from the first communication apparatus.

(Supplementary Note 30)

The first communication apparatus according to any one of SupplementaryNotes 1 to 29, wherein

the second communication apparatus is an apparatus connected to theplurality of antennas, and

the first communication apparatus is an apparatus connected to thesecond communication apparatus.

(Supplementary Note 31)

The first communication apparatus according to any one of SupplementaryNotes 1 to 30, wherein

the first communication apparatus is an apparatus located indoors, and

the second communication apparatus is an apparatus located outdoors.

(Supplementary Note 32)

A second communication apparatus comprising:

a radio communication processing unit configured to receive signals viaa plurality of antennas;

a transmission processing unit configured to transmit, to a firstcommunication apparatus, channel related information related to achannel of signals received via the plurality of antennas; and

reception processing unit configured to receive, from the firstcommunication apparatus, weight information related to reception antennaweights, the weight information being generated based on the channelrelated information,

wherein the radio communication processing unit is configured tomultiply signals received via the plurality of antennas by the receivingantenna weights.

(Supplementary Note 33)

A method comprising:

receiving, from a communication apparatus which receives signals via aplurality of antennas, channel related information related to a channelof signals received via the plurality of antennas; and

transmitting, to the communication apparatus, weight information relatedto receiving antenna weights by which the communication apparatusmultiplies signals received via the plurality of antennas, the weightinformation being generated based on the channel related information.

(Supplementary Note 34)

A method comprising:

receiving signals via a plurality of antennas;

transmitting, to a communication apparatus, channel related informationrelated to a channel of signals received via the plurality of antennas;

receiving, from the communication apparatus, weight information relatedto reception antenna weights, the weight information being generatedbased on the channel related information; and

multiplying signals received via the plurality of antennas by thereceiving antenna weights.

(Supplementary Note 35)

A program that causes a processor to execute:

receiving, from a communication apparatus which receives signals via aplurality of antennas, channel related information related to a channelof signals received via the plurality of antennas; and

transmitting, to the communication apparatus, weight information relatedto receiving antenna weights by which the communication apparatusmultiplies signals received via the plurality of antennas, the weightinformation being generated based on the channel related information.

(Supplementary Note 36)

A program that causes a processor to execute:

receiving signals via a plurality of antennas;

transmitting, to a communication apparatus, channel related informationrelated to a channel of signals received via the plurality of antennas;

receiving, from the communication apparatus, weight information relatedto reception antenna weights, the weight information being generatedbased on the channel related information; and

multiplying signals received via the plurality of antennas by thereceiving antenna weights.

(Supplementary Note 37)

A non-transitory computer readable recording medium having recordedthereon a program that causes a processor to execute:

receiving, from a communication apparatus which receives signals via aplurality of antennas, channel related information related to a channelof signals received via the plurality of antennas; and

transmitting, to the communication apparatus, weight information relatedto receiving antenna weights by which the communication apparatusmultiplies signals received via the plurality of antennas, the weightinformation being generated based on the channel related information.

(Supplementary Note 38)

A non-transitory computer readable recording medium having recordedthereon a program that causes a processor to execute:

receiving signals via a plurality of antennas;

transmitting, to a communication apparatus, channel related informationrelated to a channel of signals received via the plurality of antennas;

receiving, from the communication apparatus, weight information relatedto reception antenna weights, the weight information being generatedbased on the channel related information; and

multiplying signals received via the plurality of antennas by thereceiving antenna weights.

(Supplementary Note 39)

A system comprising:

a first communication apparatus; and

a second communication apparatus,

wherein the second communication apparatus is configured to:

-   -   receive signals via a plurality of antennas; and    -   transmit, to the first communication apparatus, channel related        information related to a channel of signals received via the        plurality of antennas,

wherein the first communication apparatus is configured to:

-   -   receive the channel related information from the second        communication apparatus; and    -   transmit, to the second communication apparatus, weight        information related to receiving antenna weights, the weight        information being generated based on the channel related        information, and

wherein the second communication apparatus is configured to:

-   -   receive the weight information from the first communication        apparatus; and    -   multiply signals received via the plurality of antennas by the        receiving antenna weights.        (Supplementary Note 40)

A method comprising:

in a second communication apparatus,

-   -   receiving signals via a plurality of antennas; and    -   transmitting, to a first communication apparatus, channel        related information related to a channel of signals received via        the plurality of antennas,

in the first communication apparatus,

-   -   receiving the channel related information from the second        communication apparatus; and    -   transmitting, to the second communication apparatus, weight        information related to receiving antenna weights, the weight        information being generated based on the channel related        information, and

in the second communication apparatus,

-   -   receiving the weight information from the first communication        apparatus; and    -   multiplying signals received via the plurality of antennas by        the receiving antenna weights.

In a mobile communication system, both a circuit scale of an apparatusthat receives signals via antennas and a band of an interface betweenapparatuses can be small.

REFERENCE SIGNS LIST

-   1, 2 System-   10 Base station-   21, 23 Communication line-   40 Terminal apparatus-   100 Digital apparatus-   131 Radio communication processing unit-   133, 610 Reception processing unit-   135 Generating unit-   137, 620 Transmission processing unit-   200 Radio apparatus-   241, 710 Radio communication processing unit-   243, 720 Transmission processing unit-   245, 730 Reception processing unit-   300, 800 Antenna-   411 Channel estimation unit-   413 Antenna weight generating unit-   600 First communication apparatus-   700 Second communication apparatus-   1001 Time frame-   1003 Specific period-   1011 Reference signals

What is claimed is:
 1. A method performed by a base band unit, themethod comprising: hosting a first physical layer; receiving referencesignals from a radio unit, wherein the radio unit is configured to hosta second physical layer being at a lower layer of a communicationprotocol than the first physical layer and receive signals via aplurality of antennas; performing channel estimation based on thereference signals; and transmitting, to the radio unit, weightinformation related to receiving antenna weights by which signalsreceived via the plurality of antennas are multiplied by the radio unit,wherein each of the base band unit and the radio unit is one of aplurality of apparatuses constituting a base station, and wherein thebase band unit and the radio unit are physically separated, and the baseband unit and the radio unit are linked by an interface requiring afrequency band.
 2. The method according to claim 1, wherein the weightinformation is information indicating the receiving antenna weights. 3.The method according to claim 2, wherein the weight information includesinformation indicating respective weights included in the receivingantenna weights.
 4. The method according to claim 2, wherein thereceiving antenna weights are one receiving antenna weight set includedin a plurality of predetermined receiving antenna weight sets, and theweight information is an index indicating the one receiving antennaweight set.
 5. The method according to claim 1, wherein the weightinformation is generated based on channel estimates calculated by thechannel estimation.
 6. The method according to claim 1 furthercomprising: transmitting, to the radio unit, the weight information andinformation related to use of the receiving antenna weights.
 7. Themethod according to claim 6, wherein the information related to use ofthe receiving antenna weights includes frequency information related tofrequencies for which the receiving antenna weights are used.
 8. Themethod according to claim 6, wherein the information related to use ofthe receiving antenna weights includes time information related to timewhen the receiving antenna weights are used.
 9. The method according toclaim 1, wherein the reference signals are reference signals transmittedduring a specific period in a time frame.
 10. The method according toclaim 9, wherein the time frame is a radio frame, and the specificperiod is a specific symbol.
 11. The method according to claim 1,wherein the reference signals are sounding reference signals (SRS) ordemodulation reference signals (DMRS).
 12. The method according to claim1 further comprising: generating the weight information based on thereference signals.
 13. The method according to claim 1 furthercomprising: performing demodulation and decoding for signals of one ormore layers generated by the radio unit multiplying signals received viathe plurality of antennas by the receiving antenna weights.
 14. Themethod according to claim 1 further comprising: transmitting, to theradio unit, other weight information related to transmitting antennaweights which the radio unit uses for generation of signals to betransmitted via the plurality of antennas, the other weight informationbeing generated based on the reference signals.
 15. The method accordingto claim 1, wherein the receiving antenna weights are antenna weightswhich the radio unit also uses for generation of signals to betransmitted via the plurality of antennas.
 16. The method according toclaim 14, wherein the radio unit is an apparatus which performscommunication in time division duplex (TDD).
 17. The method according toclaim 1, wherein the receiving antenna weights are weights by which theradio unit multiplies signals from the terminal apparatus, the signalsbeing received via the plurality of antennas.
 18. The method accordingto claim 1 further comprising: transmitting, to the radio unit, otherweight information related to transmitting antenna weights, and whereinthe other weight information related to transmitting antenna weights isinformation in a format the same as a format of the weight informationrelated to the receiving antenna weights.
 19. A method performed byradio unit comprising: hosting a second physical layer being at a lowerlayer of a communication protocol than a first physical layer; receivingsignals via a plurality of antennas; transmitting, to a base band unit,reference signals to be used for channel estimation performed by thebase band unit, wherein the base band unit is configured to host thefirst physical layer; receiving, from the base band unit, weightinformation related to reception antenna weights, and multiplyingsignals received via the plurality of antennas by the receiving antennaweights, wherein each of the base band unit and the radio unit is one ofa plurality of apparatuses constituting a base station, and wherein thebase band unit and the radio unit are physically separated, and the baseband unit and the radio unit are linked by an interface requiring afrequency band.
 20. A base band unit comprising: a memory storinginstructions; and one or more processors configured to execute theinstructions to: host a first physical layer; receive reference signalsfrom a radio unit, wherein the radio unit is configured to host a secondphysical layer being at a lower layer of a communication protocol thanthe first physical layer and receive signals via a plurality ofantennas; perform channel estimation based on the reference signals; andtransmit, to the radio unit, weight information related to receivingantenna weights by which signals received via the plurality of antennasare multiplied by the radio unit, wherein each of the base band unit andthe radio unit is one of a plurality of apparatuses constituting a basestation, and wherein the base band unit and the radio unit arephysically separated, and the base band unit and the radio unit arelinked by an interface requiring a frequency band.